Electro-drilling method and apparatus



April 20, 1965 E. SARAPUU 3,179,187

ELECTRO-DRILLING METHOD AND APPARATUS Filed July 6. 1961 4 Sheets-Sheet1 INVENTOR April 20, 1965 E. SARAPUU ELECTED-DRILLING METHOD ANDAPPARATUS Filed July 6, 1961 4 Sheets-Sheet 2 INVENTOR f/v'ofi Sara nayATTORNEY April 20, 1965 E. SARAPUU 3,179,187

ELECTRO-DRILLING METHOD AND APPARATUS Filed July 6, 1961 4 Sheets-Sheet5 E. SARAPUU ELECTRO-DRILLING METHOD AND APPARATUS.

April 20, 1965 4 Sheets-Sheet 4 Filed July 6, 1961 INVENTOR 50/4 4/0ATTORNEY United States Patent F 3,179,187 ELECIRO-DRELLENG METHGD ANDAPPARATUS Erich Sarapuu, Kansas City, Mo., assignor to ElectrofracCorporation, a corporation of Delaware Filed July 6, 1961, Ser. No.122,172

Claims. (Cl. 175-16) This invention relates to electrical drillingdevices and processes and refers more specifically to such devices andprocesses utilizing thermal shock (successive heating and cooling)rather than heat alone whereby to effect the rock and drillingpenetration.

In the art of drilling into or penetrating earth formations and rockstructures, it is' well known to utilize electric arcs to melt into thestructure desired to be penetrated. Additionally, it is known to utilizecirculating fluids in conjunction therewith to clear the arc area andcarry off cuttings, spellings, etc. It is further old to drillelectrically while maintaining a pressure in the Wellbore in excess ofthe rock pressure whereby to drive molten rock back into the formation.Withdrawal of molten, electrically drilled material from the wellbore isadditionally known by fluid circulation of same to the surface. Stillfurther, it is known to utilize electrical are cutting means with airblowing or water supply means associated therewith to simultaneouslyheat and cool the rock surface to disintegrate same.

The above-noted electrical arc drilling art finds its reflectedcounterpart in the older flame blast, gas flame or burner drilling art,which is of more ancient derivation. It has been long known toalternately apply gas blast and a cooling medium against a rock facewhereby to disintegrate the rock by thermal shock in this manner.Circulation of liquids to carry cuttings and spallings out of the way ofthe cutting operation is also well known in this art. Mechanical meansare often employed with the flame blast drilling means to aid inbreaking up slag created by the drilling blast. It is additionally knownto utilize, in a drill bit, air blast nozzles or cooling fluid nozzlesspatially alternated with heated gas blast nozzles whereby flame contactis followed by cooling fluid contact with circulation of mud or thecooling fluid to remove cuttings. Mechanical cutters may also beassociated with such a drill head. Rotating fiame blow pipes withsimultaneous water injection to carry away slag are additionally known.

An object of the invention is to provide an improved electrical drillingdevice which utilizes a heating-cooling cycle which operates todistintegrate the rock or earth formation through which the drill ispassing and provide an effective drilling or coring means.

Another object of the invention is to provide an improved electricallydriven forced heating and cooling cycle which powders or disintegratesthe rock particles away from the natural cementing material therebetweeninstead of electrically melting it.

Another object of the invention is to provide an improved electricaldrilling device whereby electrical currents are discharged from thedrill bit through direct contact between the drill bit and the rock orground structure.

Another object of the invention is to provide an improved electricaldisintegrating drilling device wherein the electrical currents beingdischarged against the bottom hole structure create electrical shockwaves which 3,179,187 Patented Apr. 20, 1%65 physically tend tofracture, pulverize and break up the rock formation.

Another object of the invention is to provide such a device whichprovides a heating zone under certain limited portions of the bit,whereby, upon rotation of the bit, to provide alternate heating andcooling of the rock thereby tending to disintegrate the material drilledfrom successive thermal shocks.

Still another object of the invention is to provide a device forelectrically drilling earth horizons and zones wherein the drill bitincludes cooling means superimposed behind rotating heating meanswhereby to cause the alternate expansion and contraction of the heatedand cooled rock zones and members whereby to effectuate heat shockdisintegration of the material being drilled.

Still another object of the invention is to provide means for imposingheating and cooling cycles on the rock structure being drilled withoutrequiring rotation of the drill bit.

Another object of the invention isto provide means for electricaldrilling wherein electrical disintegration effects extend laterally, toa certain extent, of the drill bit as well as downwardly therefrom.

Another object of the invention is to provide an electricaldisintegrating drilling device wherein a fluid medium passed centrallyof the tubing or other means support ing the drill bit serves to carrycutting and debris out of the way of the drilling operation.

Another object of the invention is to provide an electricaldisintegrating drilling means which permits effective drilling andcoring with actual contact. between the bit and the material orformation being drilled.

Another object of the invention is to provide electrical disintegratingdrilling means which are suitable for commercial application and whichprovides high speed drilling penetration into hard rock formations.

Another object of the invention is to provide electrical currentdrilling means which may be designed slightly eccentric in form wherebyto wabble rotation, if rotation is employed, whereby to drill a muchlarger diameter borehole than one might expect from the bit diameterand. wherein undercutting may also be achieved, if desired.

Another object of the invention is to provide an electrical currentdrilling means wherein suificientelectrical discharge takes placelaterally in the borehole whereby to encrust or fuse the sides or wallsof the borehole as drilling or coring proceeds.

Other and further objects of the invention will appear in the course ofthe following description thereof.

In the drawings, which form a part of the instant specification and areto be read in conjunction therewith,

embodiments of the invention are shown and, in the various views, likenumerals are employed to indicate like parts.

FIG. 1 is a view above and cross sectionally through a portion of anearth horizon illustrating a first form of electrical drilling apparatuspenetrating the horizon with the means for operating the drillingapparatus positioned on the surface.

FIG. 2 is a sectional view through an earth horizon showing a secondform of electrical drilling apparatus penetrating the said horizon, theapparatus for operating same positioned at the surface.

FIG. 3 is a sectional view through an earth formation showing apparatusfor drilling laterally thereinto penetrating same, the apparatus foroperating this modification of the electrical drilling apparatuspositioned on the surface to the side of the structure being drilled.

FIG. 4 is a cross-sectional view through an earth formation showing anenlarged partly sectional view of the drill head and surface debris andcutting conduit of the drilling means.

FIG. 5 is a view of the underside of the drilling head of FIG. 4.

FIG. 6 is a view taken along the line 66 of FIG. 5 in the direction ofthe arrows.

FIG. 7 is a view taken along the line 77 of FIG. 6 in the direction ofthe arrows.

Referring first to FIG. 1, at 10 is generally designated the cab housingof a truck having a body 11 adapted to carry and mount the electricaldrilling means to be described. Positioned upon deck 12 of the truckbody 11 is an electrical generator 13 which is driven from power source14 which may be any suitable internal combustion motor. Positioned ontop of the motor 14 is air compressor 15. Ground lead 16 from connection17 on generator 13 passes to a suitable ground means 18 such as a steelbar which may be of any desired shape or size necessary to handle theelectrical load in the process to be described. A flat surface plate ofsteel with a pinrality of depending ground penetrating spikes will alsosuflice. A second output electrical lead 19 is connected to thegenerator by connection 29.

A suitable derrick construction having vertical legs .21-24, inclusive,and horizontal support bars and 26 connecting the same to one another isfixed to the rear deck of the truck. A steel plate or panel 27 slidesvertically between vertical legs 21 and 24 controlled in such motion bychains 28 and 29 connected to a suitable power source such as anelectric motor or gasoline winch at the wise powered from anyconventional power source. Drill pipe or tubing 31 passes from its upperend connection to the rotating means downwardly through nonrotating,lower fitting 32 on rotating device 30. Platform 33 receives drill pipe31 therethrough for vertical and rotational motion whereby to stabilizesame. An opening 34 defined by an insulating bushing is formed throughplatform 33 of sufficient size to permit passage of the drill pipejoints 31:: and/or centralizers therethrough. The bushing insulates thedrill pipe from the truck body. Suitable means (not shown) may beprovided for gripping the drill pipe sections already in the hole tostabilize them while another section of drill pipe is added onthereabove or other suitable conventional means in the man ner of aconventional oil derrick may be provided adjacent the top of the derrickon the truck for adding and removing sections of drill pipe to and fromthe drill string.

A compressed air hose 35 passes from air compressor 15 into uppernonrotating conventional pressure fitting 36 of drill pipe rotatingdevice 30 and is received in any conventional pressure seal fittingtherewithin whereby compressed air or other fluid may be passed into therotating drill pipe 31 for purposes to be described. Power lead 19passes from the generator into lower nonrotating fitting 32 and connectselectrically to rotatable drill pipe 31 by a conventional brush powertake-off or the like whereby the rotating drill pipe can carry theelectrical current required in the electrical drilling operation. Thedrill pipe joints 31a may be themselves covered by electricallyinsulating material for centralizing purposes or additional insulatingcentralizers of ceramic or other electrical insulating material may beprovided as at 37 to avoid lateral tubing-wall arcing and contact. Thedrilling head construction detailed in FIGS. 47, inclusive, isdesignated 33 at the lower end of drill pipe 31.

A deflector for passing rock particles, cuttings, etc. to the side ofthe borehole is generally designated 39 and has wellbore capping hood 4dat the lower end thereof, optionally electrically insulated passage orfitting 41 through the upper portion thereof extending axially of hood4% and ejection pipe 42 extending laterally thereof. This constructionor the equivalent thereof may also be employed with a conventionalwellhead structure in cooperation with suitable well casing, if thedepth of the drilling warrants. In adidtion to insulating fitting orpassage 41, which receives drill pipe 31 therein for rotation thereof,the drill pipe itself may be insulated in its entire length on theoutside thereof as seen in FIG. 4 alone, or in addition to insulation ofthe inside surface of fitting 41. The entire means 39 may be made ofelectrically insulating material, if desired. Means 33 may additionallybe formed in joinable halves to put around the top of the drill pipeafter insertion of the drill pipe in the ground with the centralizers31a and 37 thereon.

In FIG. 1, ground surface is designated 43, the earth formationtherebelow 44 and the wellbore drilled therethrough 45. Cuttings anddebris from the wellbore are designated at 46.

Referring to FIG. 2, therein is shown an earth forma tion with groundlevel 47, formation proper 48 and wellbore 49 already partially drilledthereinto. A derrick generally designated 50 having vertical legs 51with lateral bracing members 52 thereon is positioned above thewellbore, has a hollow center and carries, on arms 53 and 54 thereof, areel or spool 55. A hollow, semi-rigid, fluid tight cable or hose ofreinforced plastic, plastic coated woven metal or the like is shown at56. Spool 55 is mounted on a suitable horizontal shaft (not seen)whereby to reel up and unreel cable 56 thereon. Cable 56 must be fluidtight under high gas or liquid internal pressure. Alternatively, cable56 may be a hollow fiexible conductor coated or clad with electricallyinsulating material.

A suitable air compressor generally designated 57 passes compressed airthrough pipe 58 which passes into the hollow center of the shaftrotatably mounting spool 55. Cable 56 is connected to said hollow centershaft at its end whereby to receive the air under pressure. Any suitableinternal combustion engine 59 drives conventional electrical generator66. Power lead 61 from generator 6 passes through a nonrotating sealfitting in the other end of the hollow shaft rotatably mounting spool 55from the air supply entrance of line 58 and thence into cable 56.- Anysuitable cable conductor is received in the length of cable 56 toconnect with the drill head 71 or a metallic pipe segment 62 carryingthe drill head supporting and rotating means. Ground lead 63 connects toany suitable metallic ground such as a steel bar 64. A conventionalconnection 65 between resilient cable 56 and rigid hollow tube 62removably supports the latter on the former. A conventional fluidturbine 66, driven by air or Well fluids moving upwardly therepast maybe fixed at the lower end of member 62 whereby to permit rotation oflower hollow, rigid member 62a, separate from member 62 and rotatablyconnected thereto by the turbine fittings. Rotation of the drive portionof turbine 66 rotates member 62 and drill head 61 (see FIGS. 48). Theupper portion of member 62 (not rotating) must be fixed relative to thewellbore as by laterally extending jack legs.

Cutting deflecting means generally designated 67 has wellbore cappinghood 68 at the lower end thereof, a suitable passage 69 in the upperportion thereof centrally of hood 63 whereby to pass cable 56therethrough and lateral flowing tube 70. This means may be employed atthe top of a conventional wellhead, if such is employed, and may behalved to fit around the tubing 56 after the drilling head 71 and itsupper fittings are passed therebelow. Centralizers (not shown) ofinsulating material may be mounted on tube 56 if desired.

Referring to FIG. 3, therein is shown an earth forma-- tion having alevel ground surface 71 adjacent a hill or cliff structure 72 with earthformation 73 therewithin. A truck bed 74 mounted on wheels 75 carriessupport frame 76 mounting spool or reel 77 for rotation upon a hollowshaft (not seen). Air compressor 78 passes commounting spool 77 througha nonrotating seal fitting and connects to a conductor within tubing 83.Ground lead 84 from generator 81 is elevated by frame 85 carryinginsulator 86 and passes to earth ground 87 lower in the earth structurethan the wellbore to be drilled.

Spool 77 mounts a coil of tubing 83 which is of the character previouslydescribed relative to FIG. 2, namely, sufficiently rigid to besubstantially self-supporting in lateral orientation, hollow, compressedair or fluid tight and carrying an electrical conductor from power lead82 to the drilling head generally designated 88. Tubing 83 is, however,sufliciently resiilent to permit winding on spool 77. Wellbore 39drilled into earth formation 73 does not require a deflecting housingover the opening thereof at 96 as the cuttings and debris can fall belowthe opening as seen at 91. Insulating spacers 830 may be employed asdesired.

Referring now to FIGS. 4-7, inclusive, it will be assumed that theapplication of the drill head to be described is inthe Well drillingconstruction of FIG. 1. Wellbore 45 is drilled into earth formation 44.Deflection means 39 has been previously described and will not beredescribed. In the structure shown, the drill pipe or tubing 31 has aninsulating sheath of plastic or other electrically insulating material31b passing downwardly the length of the drill pipe or tubing to thedrill head generally designated 38.

Referring to the detailed construction of the drilling head, it isentirely constructed of electricity-conducting material such as steel.The upper end 92 is externally threaded as at 93 whereby to engage theinternally threaded lower end of the drill pipe 31 at 310. Upper portion92 has hollow fluid carrying passage 94- axially thereof. Anintermediate portion 95 of truncated cone form in transverse verticalsection is connected to the lower end of portion 92 and has taperedvertical wedges 96 extending vertically on the outer surface thereof,tapered outwardly to sharp edges and angled outwardly downwardly. Theouter edges of wedges 96 pass current discharges to the lateral walls ofthe wellbore and the valleys therebetween permit the passage of cuttingsupwardly there-through. Drilling surface or plate 97 has a plurality ofpassages 98 therethrough lined with hard steel tubes 99. Plate 97 may benotched to correspond with wedges 96. A plurality of parallel,transverse, sharp-edged Wedges 1%, 101 and fill extend across the lowerface of the drill plate. Wedges it'll) and 162 are of equaldownwardextension from plate 97, while wedge ltli has greater downwardextension, preferably, than both. The openings or passages. 93 arepreferably positioned in parallel lines between wedges liltl and M2 andwedge ltlll, as seen in FIG. 5. A pair of minor wedges 103 and 104 arepreferably positioned normal to the Wedges 1% and 102, outboard thereof,and centrally thereof.

In operation of the devices of the figures, the drilling head is loweredinto the wellbore by means of a drilling tubing or pipe or flexiblecable as shown in the various forms described previously. Once thedrilling head approaches the bottom of the wellbore, the electricalcurrent is turned on from the generator and its power source and,additionally and simultaneously, circulation of fluid under pressure isbegun downwardly through the drill pipe or cable. The air or fluid flowsthrough passage 94, through intermediate head portion 95 and out throughthe passages or openings 98. As the drill plate 97 and the drill head isrotated or not.

. reference to other features and subcombinations.

the Wedges lull-104, inclusive, closely approach the bottom of thewellbore, electrical discharges to the rock take place by virtue ofionization of the gaseous medium passing out of the openings of thedrill head to the wellbore bottom and also through ionization of earthmoisture. Due to the continuous flow of high pressure air or othercooling medium, each electrical discharge at 'a given spot is followedby a blast of air or other fluid medium whereby a heating-cooling cycleis set up, whether It is preferred that the drill head be rotated tovary the pattern of electrical and fluid impacts in the bottom of thewellbore.

When the drill head contacts the rock in rotation, electrical dischargestake place. Rotation alone of the drill head permits more or lesscontinuous bottom hole contact. it is preferred to vertically oscillatethe drill head suiiiciently far upwardly from the bottom of the wellborethat free passage of the fluid ionizing medium between the drilling headand the rock being drilled occurs if there is any problem of fluidcirculation. This also permits the picking up of the debris and rockparticles by the fluid medium and passing of same up the wellbore andout therefrom. In the event that the drilling head approaches thewellbore side Wall, or perhaps to a certain extent in any case, thereare lateral discharges which serve to fuse and coat the wellbore wall,as well as disintegrate same laterally.

If the drillinghead is canted on the end of the cable or drill pipe,rotation of same will cause the formation of a larger diameter wellborethan the diameter of the drilling head itself. When the drilling head isrotated as in certain of the modifications described, the wedgesliiilii2- precede, as well as the wedges 193 and 104, the following airblast jets so that, in addition to the time sequential heating coolingcycle, there is also a spacesequential heating and coolingcycleattacking the wellbore wall and bottom. The inward tapering of thedrilling head as seen at 96 upwardly concentrates the electricaldischarges at the lower end of the drill head. By having the centralWedge lltll of greater depth than the adjacent wedges, the greatestdepth of drilling is accomplished centrally of the wellbore bottomwhereby the particles of the debris may be blasted upwardly past theinwardly tapering drilled surface. A stronger concentration ofelectrical force is also obtained from the greater depth wedge. However,this is preferred, not required.

As the rock conductively varies and also thequantity of earth and bottomhole moisture, it may be desirable to circulate steam, water or drillingmud through the head to aid ionization. In such case, the casing must besheathed with insulation.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure.

It will be understood that certain features and subcombinations are ofutility and may be employed without This is contemplated by and iswithin the scope of the claims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the'accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having'thus described my invention, I claim:

1. A process. of electrically drilling subsurface wellbores comprisingpositioning an electrical current carrying drill head in a wellbore witha portion of said drill head in physical contact with the bottom orterminus of-said wellbore, said drill head carried by a drill stemextending downwardly into the earth formation from the surface,continuously flowing electrical current through said drill head into thesaid wellbore terminus in at least one narrow transverse strip Zoneextending across the bottom of the wellbore, the drill head portioncontacting the wellbore terminus comprising a substantially continuouselongate edge or line element mounted on the underside of said drillhead and extending substantially across the bottom of said wellbore,said electrical current continuously flowed through said edge or lineelement in quantities sufficient to strongly heat the said terminustransverse strip zone in a substantially continuous manner throughoutits entire extent by the electrical phenomenon of contact resistance ofa ground electrode, rotating said drill head and line or edge elementthereon around a central axis substantially corresponding to the centralaxis of the wellbore and simultaneously flowing an elongate narrowtransverse stream of cooling fluid through said drill head in suchmanner that said transverse stream of cooling fluid follows and contactsin close sequence the said heated transverse terminus strip, whereby asubstantially circular, continuous, sequent heating and cooling patternis initiated and maintained in a circular Zone at the bottom or terminusof the wellbore, said circular zone penetrating continuously deeper intothe earth formation as the drill head underside-wellbore terminuscontact, rotation of the drill head and line element thereon, andelectrical current and fluid flow through the drill head are maintained.

2. A process of drilling subsurface wellbores comprising positioning anelectrical current carrying drill head in a wellbore with a limitedportion thereof in physical contact with the bottom or terminus thereof,said drill head carried at the end of a drill stem communicating thelength of the wellbore from the surface, continuously flowing electricalcurrent through said drill head into the earth formation at the wellboreterminus in a plurality of narrow substantially parallel transversestrip zones extending substantially across the terminus or bottom of thewellbore, the drill head portion contacting the terminus comprising aplurality of substantially continuous line or edge elements on theunderside of said drill head each extending substantially entirelyacross the drill head underside and bottom or terminus of the wellbore,said electrical current continuously flowed through said drill head andline or edge elements thereon in quantities suflicient to markedly heatthe said narrow transverse strip zones in a substantially continuousmanner across their entire extent by the electrical phenomenon ofcontact resistance of ground electrodes, rotating said drill head andline or edge elements thereon around a central axis substantiallycorresponding to the central axis of the wellbore and simultaneouslyflowing a plurality of elongate transverse bands of cooling fluidthrough the underside of said drill head in such position and pattern asto closely follow and contact in following sequence the electricallyheated transverse earth formation strip zones, whereby a circular,continuously moving, sequent, transverse earth formation heating andcooling action is initiated and maintained in a circular zone at thebottom of the wellbore, said circular zone penetrating continuouslydeeper into the earth formation as the drill head underside-wellborecontact, rotation of the drill head and line or edge elements thereonand current and fluid flow therethrough are maintained.

3. A process of drilling subsurface wellbores comprising positioning acurrent carrying drill head in earth formation contact at the bottom orterminus of a wellbore, said drill head mounted on a drill sterncommunicating from the surface to said wellbore terminus, continuouslyflowing electrical current into the earth formation at the wellboreterminus through the drill head contact therewith in a plurality ofnarrow transverse strip zones extending across the bottom of thewellbore, the underside of the drill head contacting the wellboreterminus through a plurality of substantially parallel and continuousline or edge elements thereon of such length as to extend substantiallyacross the bottom or terminus of said wellbore, said currentcontinuously flowed through said drill head and line elements thereon inquantities suflicient to markedly heat the said narrow transverse stripzones in a substantially continuous manner across their entire extent bythe elec trical phenomenon of contact resistance of ground electrodes,rotating said drill head and line or edge electrode elements thereonaround a central axis substantially corresponding to the central axis ofthe wellbore and simultaneously continuously flowing an elongatetransverse narrow stream of cooling fluid through the underside'of saiddrill head and between each pair of said line elements in such quantity,velocity and manner as to continuously follow and contact the heatedtransverse strip zones with said fluid stream, whereby a circular,continuously rotating, sequent, earth formation heating and coolingaction is initiated and maintained in a circular zone at the bottom orterminus of the wellbore, said circular zone penetrating continuouslydeeper into the wellbore terminus earth formation as the drill headunderside-wellbore terminus contact, rotation of the drill head and lineelements thereon, and current and fluid flow therethrough aremaintained.

4. A process of drilling subsurface wellbores comprising positioning anelectrical current carrying drill head in a wellbore with the undersidethereof in physical contact with the earth formation at the bottom orterminus of said wellbore, said drill head carried by a drill stemextending from the surface the length of said wellbore, continuouslyflowing electrical current into the earth formation at said wellboreterminus through said drill head wellbore contact in at least one narrowtransverse strip zone extending substantially across the diameter of thewellbore, the

drill head underside portion contacting the wellbore terminus comprisingat least one elongate, substantially continuous line or edge electrodeelement, said electrical current continuously flowed through said drillhead line element into said zone in quantity sufiicient tomarkedly anddeeply heat same in a substantially continuous manner through and alongits entire diametric extent by the electrical phenomenon of contactresistance of a ground electrode, simultaneously continuously flowingquantities of cooling fluid downwardly through the underside of saiddrill head, said fluid flow passing out of said drill head in anelongate continuous line positioned substantially parallel to andclosely on one side of said line element whereby said earth formationtransverse strip zone is subjected to continuous, juxtaposed electricalheating action and cooling fluid flow thereat, the flow of electricalcurrent into the terminus earth formation through said drill head lineelement and the adjacent and coacting flow of cooling fluid also movingthrough said drill head effecting downward penetration of said drillhead continuously deeper into the earth formation as theelectrode-terminus contact, and electrical current and fluid flow aremaintained.

5. A process of drilling subsurface wellbores comprising positioning anelectrical current carrying drill head in a wellbore with a limitedportion of the underside thereof in physical contact with the earthformation at the wellbore bottom or terminus, said drill head carried bya drill stem extending the length of the wellbore from the surface tosaid terminus, continuously flowing electrical current into portions ofthe earth formation at the wellbore terminus, said current flowed into aplurality of narrow transverse strip zones extending in substantiallyparallel array across the wellbore terminus, the drill head undersideportions contacting the earth formation comprising a plurality ofelongate substantially continuous line or edge electrode elements eachextending substantially continuously across the drill head underside andalso substantially across the entire bottom or terminus of saidwellbore, said electrical current flowed into the earth formationthrough said line elements in quantities sufficient to markedly andpenetratingly heat the said earth formation transverse strip zonesthroughout their entire extent by the electrical phenomenon of contactresistance of ground electrodes, simultaneously continuously flowing atleast one transversely extending band or line of cooling fluiddownwardly through the underside of said drill head and between eachpair of earth formation contacting drill head edge elements, said lineof cooling fluid extending substantially parallel to said line elementsand of transverse extent at least substantially as great as same,whereby continuously acting electrical heating and fluid 5 coolingeffects in the terminus earth formation are initiated and thereaftercontinuously maintained in a transverse zone at the Wellbore terminusand whereby to cause said drill head to penetrate continuously deeperinto the earth formation so long as the electrode-earth formation con-10 tact and current and fluid flow are maintained.

References Cited by the Examiner UNITED STATES PATENTS 416,873 12/89Tilghman 219-68 XR 15 Sutton 17516 Armstrong 219--68 Signell et a1.175418 Clark 175-16 Dobie 17516 XR Murray 175-16 Murray 17516 XR Murray175-46 XR Allen 17516 Inoue 219-68 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

1. A PROCESS OF ELECTRICALLY DRILLING SUBSURFACE WELLBORES COMPRISINGPOSITIONING AN ELECTRICAL CURRENT CARRYING DRILL HEAD IN A WELLBORE WITHA PORTION OF SAID DRILL HEAD IN PHYSICAL CONTACT WITH THE BOTTOM ORTERMINUS OF SAID WELLBORE, SAID DRILL HEAD CARRIED BY A DRILL STEMEXTENDING DOWNWARDLY INTO THE EARTH FORMATION FROM THE SURFACE,CONTINUOUSLY FLOWING ELECTRICAL CURRENT THROUGH SAID DRILL HEAD INTO THESAID WELLBORE TERMINUS IN AT LEAST ONE NARROW TRANSVERSE STRIP ZONEEXTENDING ACROSS THE BOTTOM OF THE WELLBORE, THE DRILL HEAD PORTIONCONTACTING THE WELLBORE TERMINUS COMPRISING A SUBSTANTIALLY CONTINUOUSELONGATE EDGE OR LINE ELEMENT MOUNTED ON THE UNDERSIDE OF SAID DRILLHEAD AND EXTENDING SUBSTANTIALLY ACROSS THE BOTTOM OF SAID WELLBORE,SAID ELECTRICAL CURRENT CONTINUOUSLY FLOWED THROUGH SAID EDGE OR LINEELEMENT IN QUANTITIES SUFFICIENT TO STRONGLY HEAT THE SAID TERMINUSTRANSVERSE STRIP ZONE IN A SUBSTANTIALLY CONTINUOUS MANNER THROUGHOUTITS ENTIRE EXTENT BY THE ELECTRICAL PHENOMENON OF CONTACT RESISTANCE OFA GROUND ELECTRODE, ROTATING SAID DRILL HEAD AND LINE OR EDGE ELEMENTTHEREON AROUND A CENTRAL AXIS SUBSTANTIALLY CORRESPONDING TO THE CENTRALAXIS OF THE WELLBORE AND SIMULTANEOUSLY FLOWING AN ELONGATE NARROWTRANSVERSE STREAM OF COOLING FLUID THROUGH SAID DRILL HEAD IN SUCHMANNER THAT SAID TRANSVERSE STREAM OF COOLING FLUID FOLLOWS AND CONTACTSIN CLOSE SEQUENCE THE SAID HEATED TRANSVERSE TERMINUS STRIP, WHEREBY ASUBSTANTIALLY CIRCULAR, CONTINUOUS, SEQUENT HEATING AND COOLING PATTERNIS INITIATED AND MAINTAINED IN A CIRCULAR ZONE AT THE BOTTOM OR TERMINUSOF THE WELLBORE, SAID CIRCULAR ZONE PENETRATING CONTINUOUSLY DEEPER INTOTHE EARTH FORMATION AS THE DRILL HEAD UNDERSIDE-WELLBORE TERMINUSCONTACT, ROTATION OF THE DRILL HEAD AND LINE ELEMENT THEREON, ANDELECTRICAL CURRENT AND FLUID FLOW THROUGH THE DRILL HEAD ARE MAINTAINED.